Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1-1-1968 Pulmonary diffusing capacity for carbon monoxide in sheep. Alberto Hugo Sillau Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Recommended Citation Sillau, Alberto Hugo, "Pulmonary diffusing capacity for carbon monoxide in sheep." (1968). Retrospective Theses and Dissertations. 18497. https://lib.dr.iastate.edu/rtd/18497 This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. PULMONARY DIFFU SING CAPACITY FOR CARBON MONOXIDE IN SHEEP S rJ~f' by S;3'l (} • -2- Alberto Hugo Sillau A Thesis Submitted to t he Graduate Faculty in Partial Fu l fillment of The Requirements for the Degree of MASTER OF SC I ENCE Major Subject: Veterinary Physiology Signatures have been redacted for privacy Iowa St ate University Ames, Iowa 1968 1481012 ii TABLE OF CONTENTS Page r. INTRODUCTION l II. REVIEW OF LITERATURE 2 I II. MATERIALS AND METillDS 24 IV• RESULTS 28 v. DISCUSSION 35 VI. SUMMARY 39 VII. LITERATURE CITED 40 VIII. ACKNOWLEDGEMENTS 47 IX. APPENDIX 48 I cm l I. ItITRODUCTION The physiology of the respiratory system in domestic animals has not been studied to the extent that its importance deserves. In many aspects not even normal values have been established. There is a definite need for a series of studies in order to establish nonnal values and techniques to pennit the clinical appreciation of the respiratory function in domestic animals . Most of the efforts in this I area have been conducted on anesthetized animals. This is unfortunate be- cause anesthetized animals are not nonnal. The estimation of pulmonary diffusing capacity is a good indicator of the efficiency of pulmonary function. It gives an estimation of the area available for diffusion and the condition of the air-blood barri er. In pulmonary adenomatosis, emphysema, and pneumonia the estimation of pulmonary diffusing capacity could be of importance in the diagnosis and prognosis . The primary objectives of this investigation were to estimate pul- monary diffusing capacity in nonnal sheep and to study the effectiveness of this measurement method in detecting artificially-produced alveolar lesions. 2 II. REVIEW OF LITERA1URE A. Symbols All of the symbols used in the present work are those based on a report in Federation Proceedings (83). These symbols were selected by a group of American pulmonary physiologists in 1950. A dash (-) above any symbol indicates a mean value. A dot (•) above any symbol indicates a time derivative. 1. Symbols for gases a) Primary symbols V = gas volume V = gas volume/unit time P = gas pressure P = mean gas pressure F = fractional concentrations in dry gas phase f = respiratory frequency (breath/unit time) 0 = diffusing capacity R = respiratory exchange ratio BP = barometric pressure b) Secondary symbols 1 = inspired gas E = expired gas ,. = alveolar gas T = tidal gas 3 o = dead space gas a = barometric STPD = 0°C. 760 nun Hg . dry BTPS = body temperature and pressure saturated with water vapor ATPS = ambient temperature and pressure saturated with water vapor 2. Symbols for blood a) Primary symbols Q = volwne of blood Q. = volume flow of blood/unit time C = concentration of gas in blood phase S = % saturation of Hb with 02 or CO b) Secondary symbols a = arterial blood v = venous blood c = capillary blood 3. Symbols for lung volumes VC =vital capacity IC = inspiratory capacity IRV = inspiratory reserve volume ERV = expir atory reserve volume FRC = functional residual capacity RV = residual volume TLC = tota l lung capacit y .. -.i.:;i 4 B. Definition of Pulmonary Diffusing Capacity The molecules of 02 and co 2, which are transferred because of their differences in partial pressure between blood and alveolar gas, cross a number of membranes and liquid interphases which present a certain resis- tance to their passage. This resistance limits the rate of diffusion from one side of the alveolar wall to the other. The simple relationship between the quantity of a gas diffusing from one medium into the other per unit of time cVX) and the difference between partial pressure of the gas in the alveolar gas (PAX) and the mean pressure of the gas in the capillary (PC.X) is given by: VX = DX(PAX-PcX) . DX is the diffusing capacity of the lung for X. When VX is in ml/min STPD, and the pressures are in nun Hg, DX becomes the volume of gas which diffuses between blood and gas per minute and per mm Hg pressure difference. VX (ml/min, STPD) DX (ml/min mm Hg, STPD) = PAX-PCX (nun Hg) Dejours (56), Comroe (57), Forster (12). c. Techniques for Measuring Pulmonary Diffusing Capacity with Carbon Monoxide The techniques most frequently used for measuring pulmonary diffusing capacity are those that use carbon monoxide. Bohr was the first to use CO (carbon monoxide) for the measurement of diffusing capacity of the lung. The idea was based on his realization that affinity of hemoglobin for CO was too great and that if one were careful to use small concentrations of CO in the inspired air, the ifuCO concentration in the blood could be ignored. r w f 5 I Bohr assumed that the rate of combination of CO with intracellular lfu was instantaneous so that the CO that diffused across into the plasma was ·immediately taken up by Hb (hemoglobin). There are three principal techniques for the determination of o~co (pulmonary diffusing capacity for CO). These are (1) steady state tech- nique, (2) breath holding technique, and (3) rebreathing technique. 1. Steady state technique There are two ways of measuring DLCO with the steady state technique as follows: a) Measuring the rate at which CO appears in the blood. Forbes et ~· (29) and Roughton (76) have used this technique. This method de- mands measurements of the rate of change of average blood COHb concentra- I, tions and total blood volume. b) Observing the rate at which CO disappears from the respired gas. This technique has been widely used and is described elsewhere (27, 35, 6). In the steady state technique the critical point is the estimation of the alveolar pressure of CO (P&CO). Forbes et al. (29) used an alveolar sampling technique to obtain P&CO. Bates et al. (6) have used the end tidal sample technique with good results. P&CO can also be calculated from the Bohr relation: (VT x PrCO) - (Vo x PxCO) P&CO = (VT - Vo) For this last equation the dead space volume is required. Bates et al. (6) have shown that P&CO calculated in this way becomes very sensitive to small ..J. 6 differences in the estimated volume of the dead space whenever tidal volume is small. The estimation of PACO from alveolar air _or from end tidal air presents the problem of the variation of PACO with time due to uneven distribution of inspired air (36) and to uneven distribution of ventilation with respect to blood flow. Finlley et al. (27) devised a method for obtaining PACO from physio- logical dead space. This necessitates the obtainance of an arterial blood sample and the measurement of PaCOz. The formula for calculating PACO has many different forms. the most simple being: PaCOz PACO = PrCO - P°ECOz (P1CO - PECO). The formula used by Finlley et ~· is: FECO - r F1CO PACO = (BP-47) 1 - r where, PaCOz - PEC02 Vo r = Paco2 = VT The value of PACO so obtained is very sensitive to small differences in the data when either the ratio PaCOz/P ECOz is large or P~CO- P ECO is large. Another factor to be detennined in calculating DLCO is the amount of CO that is diffusing into the blood. The equation used by Finlley --et al. (27) was as follows: D J 7 FE N2 vco = VE (F1CO F1 N2 - FECO). Forster et al. (33) have determined that the rate of CO uptake in milliliters per minute depends upon the inspired PCO, total minute ventila- tion, alveolar ventilation, and total DLCO; this also assumes that these variables are uniformly distributed throughout all the alveoli in the lung. The percentage of the inspired CO that is taken up by the blood over a period of several minutes gives an index of diffusing capacity which is called fractional CO uptake (27) . CO uptake (ml/min) Fractional CO upt ake = CO inspired (ml/min) x 100 Bates (5) measured fractional CO uptake. They found it to be 53% in young people and 47% in people with average age of 59 . Finlley ( 27) found fractiona l CO upt ake to range between 42% to 61%. Comroe (17) mentions that a fractiona l CO uptake of less t han 30% i s indicative of impainnent of diffus ion. Forster et al. (33) have shown that the fractional CO upt ake is inde- pendent of the inspired CO tens ion and is therefore a function of total ventilation, alveolar ventilation, and DL CO . The fact that fractional CO uptake depends on alveolar and total ventilation makes it a poor estimation An important question is how long should the anima l breathe the mixture of gases containing CO to reach the so-ca lled steady state? Forster et al. (33) , considering respiration a continuous process and assuming a homogeneous . I • 8 lung breathing from a mixture of gases containing CO, stated that theo- retically the PAC O exponentially approaches a steady state.